Image forming apparatus such as electrophotographic apparatus and electrostatic recording devices form an image through a process including: developing a latent electrostatic image formed on a photoconductor with a developer containing a toner to thereby form a toner image; transferring the toner image onto a recording medium such as paper; and fixing the toner image on the recording medium by application of heat and pressure.
In recent years, there is a need to form high-quality images, and toners are designed for making image quality higher. In order to respond to such a need to form high-quality images, attempts have been made to make the diameters of toner particles smaller and reproduce a latent image with fidelity.
A widely employed method for producing fine particles having small particle diameters such as toner particles is a polymerization method where fine particles are formed in an aqueous medium. Toner fine particles obtained by the polymerization method generally have the following features: they are small in particle diameter and their particle size distribution is narrow; and the shape of the particles is close to a spherical shape. The polymerization method, however, has a drawback that it requires a lot of time, water and energy. Specifically, it takes a long time to complete the polymerization process, and also it has to be repeated to separate toner fine particles from a solvent after completion of solidification and then wash and dry the toner fine particles.
As an alternative method to the polymerization method, development has been made on a so-called spray granulation method (see, for example, PTLs 1 to 4). The spray granulation method is a method where toner fine particles are obtained by forming a liquid containing toner raw materials dissolved or dispersed in an organic solvent into fine particles using various atomizers, followed by drying. This spray granulation method does not have to use water, enabling considerable reduction of steps for washing and drying.
In the methods for producing fine particles described in PTLs 1 to 3, however, after spraying of a toner material liquid and before drying of liquid droplets formed, the liquid droplets are coalesced together and a solvent is dried in this state to form toner particles in some cases. Therefore, there is a problem that the formed toner particles result in having a broad particle size distribution.
The toner production method described in PTL 4 may involve the following unfavorable phenomenon when a spraying step is continuously performed. Specifically, discharging from some discharge holes stops, and a toner material liquid is flown through these discharge holes and stops discharging from other discharge holes. That is, there is a problem that discharge efficiency and stability of a toner material liquid are low.